1. Technical Field
The proposed invention relates generally to a mobility management method for use in a wireless communication system; and more particularly to a method for determining registration areas in a wireless communication system.
2. Related Art
There has been a very rapid growth in the number of service areas and subscribers in the wireless communications industry. The service requests (call attempts) received by mobile switching centers (MSC's) have been huge and kept growing especially in metropolitan areas. Therefore, mature and efficient Location (Mobility) Management plays a significant role in the regular operation of a wireless communication system.
Location (Mobility) Management is the procedure of keeping track of and locating mobile stations (MS's) in a wireless communication system so that calls arriving for them can be routed correctly to their current location. The purpose of Location (Mobility) Management is then to track the MS's using minimum overhead traffic. Since the radio bandwidth is a scarce resource in mobile radio communication systems, it's thus imperative to develop efficient techniques for minimizing this overhead traffic and thereby maximizing the revenue-generating traffic-carrying capacity of the system.
The MSC, though keeping track of MS's currently operating in its service area via a visitor location register (VLR) database, doesn't usually have accurate info as to the precise geographical location of each of the MS's within the service area. Consequently, when a call is initiated to a MS within the service area, a page must be broadcast over all cells in the service area. The paging message then has to be replicated a corresponding number of times and sent to each cell, but since there's only one cell in the system receiving a response from the MS, it means that a huge amount of radio bandwidth resources, thus additional costs, are over-wasted, which would otherwise be used for performing other tasks.
The conventional solutions to overcome this problem are to partition the service area of the wireless communication system into a plurality of registration areas (RA's), which are smaller than the service area. When a MS goes across the border of a RA and enters another RA, it will perform a location update (LU) indicating that it is operating within the newly entered RA. In this case, when a call is initiated to the MS, only the cells of that specific RA will be paged. But on the other hand, the number of LU's (with corresponding costs) will also be higher since the movements from one RA to another are more frequent. Therefore, a trade-off between paging and LU appears, and thus optimal RA formulation, i.e. the optimal determination of the boundaries (the location of borders between RA's) and the number of RA's are then very crucial.
Although the concept is caught and technically put into practice by the conventional methods, however, most of them actually just came up with a locally optimal solution, which will be explained in detail in the following paragraphs of the specification.